My understanding is that it was due to the moon being full which caused them to not have as much of an ability to observe it during the past few estimations. In an article[0] linked from the above link they state:
> Now that skies are darker after a week of limited visibility around full moon, astronomers have resumed observations
The estimates changed a lot because they were being very transparent about the information as they were discovering it.
Not "worrying" in a rational sense (i.e. we should put more thought into the possibility of this collision), but in a human emotional sense ("if NASA engineers can change their minds this quickly, surely we don't know nearly as much as we think, and the universe feels like a scarier place again").
> Now that skies are darker after a week of limited visibility around full moon, astronomers have resumed observations
The estimates changed a lot because they were being very transparent about the information as they were discovering it.
[0]: https://blogs.nasa.gov/planetarydefense/2025/02/19/dark-skie...